This invention relates to color picture tubes having tensioned masks, and particularly to a tube having means for connecting a tensioned mask, that is made of a material having a relatively low coefficient of thermal expansion material, to a support frame, that has a significantly higher coefficient of thermal expansion at normal operating temperature, but wherein the mask material has a coefficient of thermal expansion at high tube processing temperatures that is close to the coefficient of thermal expansion of the frame at the same processing temperatures.
A color picture tube includes an electron gun for generating and directing three electron beams to the screen of the tube. The screen is located on the inner surface of a faceplate of the tube and is made up of an array of elements of three different color emitting phosphors. A color selection electrode, which may be either a shadow mask or a focus mask, is interposed between the gun and the screen to permit each electron beam to strike only the phosphor elements associated with that beam. A shadow mask is a thin sheet of metal, such as steel, that is usually contoured to somewhat parallel the inner surface of the tube faceplate.
One type of color picture tube has a tensioned mask mounted within a faceplate panel thereof. In order to maintain the tension on the mask, the mask must be attached to a relatively massive support frame. Although such tubes have found wide consumer acceptance, there is still a need for further improvement, to reduce the weight and cost of the mask-frame assemblies in such tubes.
It has been suggested that a lighter frame could be used in a tensioned mask tube if the required tension on the mask is reduced. One way to reduce the required mask tension is to make the mask from a material having a low coefficient of thermal expansion. However, a mask from such material would require a support frame of a material having a similar coefficient of thermal expansion, to prevent any mismatch of expansions during thermal processing that is required for tube manufacturing, and during tube operation. Because the metal materials that have low coefficients of thermal expansion, such as INVAR(copyright) (nickel-iron alloy), are relatively expensive, it is rather costly to make both the mask and frame out of identical or similar low expansion materials. Therefore, it is desirable to use the combination of a low expansion tensioned mask with a less expensive higher expansion support frame. However, such a mismatch in thermal expansion coefficients requires a solution to the problem that exists when there is a substantial mismatch in coefficients of thermal expansion between a tensioned mask and its support frame. Although there have been many suggested solutions to this mismatch, those solutions have proven to be either difficult to achieve or quite expensive. Therefore, there is still a need for other solutions to the mask and frame materials selections.
The present invention provides an improvement in a color picture tube having a tensioned mask supported by a frame mounted within the tube. The frame is constructed of a carbon or low alloy steel material, and mask is constructed of a nickel alloy material that expands substantially less per unit length than does the frame in the normal operating temperature range of said tube, and expands substantially the same per unit length as said frame in the higher thermal cycling temperature range used during of tube processing.